The primary objective of this study is to investigate the roles of parathyroid hormone and calcitonin in calcium metabolism in normal children and in children with a variety of disorders of mineral and bone metabolism. We will attempt to evaluate the role of these hormones in normal growth and development. Disorders of mineral metabolism that will be studied include neonatal hypocalcemia, anti-convulsant osteomalacia, hypocalcemia associated with hypomagnesemia, chronic renal disease and metabolic bone disease. We will attempt to better characterize and determine the physiologic significance of the circulating parathyroid hormone fragments. Parallel studies will be carried out in experimental animals in an attempt to provide better insight into problems of calcium metabolism in man.